This disclosure relates to an image forming apparatus and a method for measuring discharge starting voltage, and more specifically to an image forming apparatus enabling proper measurement of discharge starting voltage by switching between voltage/current lines to a magnetic roller, and the method for measuring discharge starting voltage.
Conventionally, image forming apparatuses, such as copiers, multifunctional peripherals, and facsimiles, are equipped with many and various kinds of techniques to ensure the stability of the quality of image formation.
For example, well-known image forming apparatuses include a bias application unit that applies bias voltage to an image bearing member. One of the typical image forming apparatuses shuts off the bias voltage for the image bearing member, and the charges on the image bearing member are discharged through a grounding terminal via a resistance. This configuration can correct and control the potential accurately and stably with time and therefore can stabilize the quality of images.
There are also conventionally well-known development devices that include an image bearing member on which an electrostatic latent image is to be formed and a toner bearing member disposed in a development area so as to face the image bearing member with required spacing. In the development devices, a developer bias voltage composed of a direct voltage superimposed on an alternating voltage is applied between the toner bearing member and image bearing member to supply the toner on the toner bearing member to the image bearing member, thereby developing an electrostatic latent image. One of the typical development devices is provided with a leaking unit that causes leakage between the aforementioned image bearing member and toner bearing member by varying a leak detection voltage applied between the image bearing member and toner bearing member, and a leak detection unit that detects leakage based on current flowing between the image bearing member and toner bearing member. This development device does not need conventionally-used expensive density sensors to detect leakage, thereby reducing the cost, and can reliably detect leakage that occurs in any positions.
Other conventionally well-known development devices include an image bearing member having a thin film layer made of an organic photoconductor material on its surface. The development devices are used in image forming operations to form an image on a recording sheet, the image forming operations including exposing the image bearing member to light to form an electrostatic latent image, and then causing developer to adhere to the electrostatic latent image to visualize the image. The development devices also include a developer bearing member that carries developer to be supplied to the image bearing member, and is configured to apply voltage to the developer bearing member to supply developer from the developer bearing member to the image bearing member. One of the typical development devices employs one-component developer and includes a detection unit that detects voltage, prior to image forming operation, when leakage occurs between the developer bearing member and the thin film layer, and a setting unit that defines the range of the voltage that does not cause leakage based on the detection results of the detection unit. Even if the spacing between the developer bearing member and image bearing member varies from device to device, or if it is changed, this development device can secure a wide allowable range of developer bias voltage and can reliably prevent leakage from occurring between the developer bearing member and image bearing member. In addition, preventing the leakage results in constant formation of excellent images.
Other conventional well-known image forming apparatuses include a photoconductor that carries an electrostatic latent image, a charging device that has a charging wire extending in parallel with an axis of the photoconductor and charges the photoconductor, a detection unit that detects leak current of the charging device, and at least one of a cleaning unit that cleans the charging wire when the detection unit detects leak current and a replacement unit that replaces the charging wire when the detection unit detects leak current. In these image forming apparatuses, the charging device includes a promoting unit that promotes leakage of the charging device and is situated at a position other than positions facing the image formation area in which the electrostatic latent image is formed. Since the charging wire is at least cleaned or replaced when a leak current occurs by the promoting unit, it is possible to prevent the progress of wire thickening, and therefore it is possible to suppress leakage which adversely influences the electrostatic latent image formed on the photoconductor. In addition, since the promoting unit is situated at a position other than positions facing the image formation area in which the electrostatic latent image is formed, the adverse affects caused by the leak current that occurs by the promoting unit on the electrostatic latent image can be reduced.
Furthermore, other conventional well-known image forming apparatuses include an image forming unit and a detection unit. The image forming unit includes a photoconductive drum that is rotatably supported and is rotated with a driving force from a driving source, a developer roller that carries charged toner, is connected to a first voltage application unit for outputting alternating voltage, and supplies toner to the photoconductive drum, a development device that supplies toner to the developer roller and supports the developer roller so as to face the photoconductive drum with a gap therebetween, and a contact member that abuts against the photoconductive drum to remove residual toner. The detection unit detects discharge between the developer roller and the photoconductive drum. In one of the typical image forming apparatuses, the development device supplies toner to the developer roller with prescribed timing and for a prescribed period of time during discharge detection in which, while the photoconductive drum rotates and the first voltage application unit stepwise varies a peak-to-peak voltage of an alternating voltage applied to the developer roller, a voltage at which discharge occurs between the photoconductive drum and the developer roller is detected. This image forming apparatus does not need to have the developer roller carry the toner thereon all the time during discharge detection, and therefore can achieve stabilization of the voltage at which electric discharge occurs, thereby reliably measuring discharge starting voltage with high accuracy. Furthermore, since the image forming apparatus supplies toner to the developer roller and the photoconductive drum with constant timing, an excessive rise in toner potential at the contact member can be prevented, and the photoconductive drum can be thereby protected from damage.